The Internet is a massive network of networks in which computers communicate with each other via use of different communication protocols. The Internet includes packet-routing devices, such as switches, routers and the like, interconnecting many computers. To support routing of information such as packets, each of the packet-routing devices typically maintains routing tables to perform routing decisions in which to forward traffic from a source computer, through the network, to a destination computer.
One way of forwarding information through a provider network over the Internet is based on MPLS (Multiprotocol Label Switching) techniques. In an MPLS-network, incoming packets are imposed with a label by a so-called LER (Label Edge Router) receiving the incoming packets. The packets in the MPLS network are forwarded along a predefined Label Switch Path (LSP) defined in the MPLS network based on label on the packets. At internal nodes of the MPLS-network, the packets are forwarded along a predefined LSP through so-called Label Switch Routers. LDP (Label Distribution Protocol) is used to distribute appropriate labels for label-switching purposes.
Each Label Switching Router (LSR) in an LSP between respective LERs in an MPLS-type network makes forwarding decisions based solely on a label of a corresponding packet. Depending on the circumstances, a packet may need to travel through many LSRs along a respective path between LERs of the MPLS-network. As a packet travels through a label-switching network, each LSR along an LSP strips off an existing label associated with a given packet and applies a new label to the given packet prior to forwarding to the next LSR in the LSP. The new label informs the next router in the path how to further forward the packet to a downstream node in the MPLS network eventually to a downstream LER that can properly forward the packet to a destination.
MPLS service providers have been using unicast technology to enable communication between a single sender and a single receiver in label-switching networks. The term unicast exists in contradistinction to multicast (or point to multipoint “P2MP”), which involves communication between a single sender and multiple receivers. Both of such communication techniques (e.g., unicast and multicast) are supported by Internet Protocol version 4 (IPv4).
Service providers have been using so-called unicast Fast Reroute (FRR) techniques for quite some time to provide more robust unicast communications. In general, fast rerouting includes setting up a backup path for transmitting data in the event of a network failure so that a respective user continues to receive data even though the failure occurs.
In multicast networks, Reverse Path Forwarding (RPF) techniques are used in building source-specific forwarding paths such that the multicast traffic can flow more efficiently without forwardwarding loops. A network employing RPF issues source-specific joins towards the source node while using the source address to look up a unicast routing table entry. This upstream process continues router by router until the source is reached. The upstream routers then are able to forward the multicast traffic downstream toward the original join. In essence, the traffic is forwarded along the reverse path from the source back to the listener.